1. Field of the Invention
This invention relates generally to citizen band antennas and, more specifically, to a citizen band (CB) antenna including means for manually adjusting the electrical length of the antenna.
2. Description of the Prior Art
Citizen band antennas are designed to receive and transmit radio waves to and from a radio which operates within a specific range of audio frequencies. The purpose of the antenna is to achieve maximum radiation and reception of transmitted or received radio signals. Therefore, it is desirable to select an antenna whose natural or resonant frequency is tuned to the frequency of the radio waves that are to be transmitted and received by the user's radio.
In the past, CB antennas have been factory tuned to a frequency approximately in the middle of the citizen band frequency range. As a result, as the user operated a radio at a frequency that was within the citizen band range but deviated from the factory tuned resonant frequency, transmitting and receiving performance faltered due to the cancellation effect of the non-resonant frequencies carried on the antenna.
To help alleviate this problem, an improved type of antenna was designed wherein the antenna could be tuned to carry a specific harmonic within the operator's desired range of frequencies. This type of prior art usually comprised a metal whip antenna which could be physically lengthened or shortened by loosening a bolt and sliding a portion of the metal whip in or out of a coil housing. Whereas this type of antenna did indeed enhance frequency response, it exhibited loss of signal power due to material and series resistance along the length of the metal antenna.
Another type of antenna was introduced that greatly improved the reception and transmission response. Signal strength was increased by using a fiberglass core around which was wound a transmission wire tuned, as before, to a frequency in the middle of the desired range of use. This type of antenna carried a signal to the receiver with very little loss of signal strength. However, this was still a non-tunable antenna and suffered from a deficient frequency response.
The need existed to design a tunable CB radio antenna that would exhibit a desirable frequency response, while suffering minimal loss or compromise in signal strength.